- AES operates on 128-bit blocks using key sizes of 128, 192, or 256 bits.
- Each round consists of SubBytes, ShiftRows, MixColumns, and AddRoundKey.
- Confusion is provided by SubBytes (S-Box) and Diffusion by ShiftRows and MixColumns.
### AES & Substitution-Permutation Networks
The Advanced Encryption Standard (AES) is a symmetric block cipher operating on a 4x4 matrix of bytes called the **State**.
#### AES Round Transformations:
1. **SubBytes**: Non-linear byte substitution using S-Box tables (Confusion).
2. **ShiftRows**: Cyclically shifts the bytes in each row of the State (Diffusion).
3. **MixColumns**: Linear transformation mixing the bytes of each column.
4. **AddRoundKey**: XORs the State with the subkey derived from key expansion.